This invention relates to dynamoelectric machines, and in particular, to single phase induction motors. While the invention is described with particular reference to motors used in hermetic compressor applications, those skilled in the art will recognize the wider applicability of the inventive principles disclosed hereinafter.
There long has been a need in the residential refrigeration market for efficient and economical equipment. The rising cost of energy, in all forms, has tended to accent this need. One area where improved efficiency can be obtained is in the sizing of the equipment itself so that efficient operation is attained over a wide range of load conditions. In the past, it has been difficult to size the equipment so that the equipment, as installed, has ample capacity for peak load conditions, yet also operates efficiently and provides comfort at lighter load conditions. Prior art solutions to the sizing problems usually involved various mechanical unloading devices in order to regulate the load to the system. The terms refrigeration and air conditioning are used interchangeably in this specification in their broadest generic sense, and are intended to include any system having a hermetic compressor as an element.
More recently, attempts have been made to modulate the compressor of the refrigeration system by operating the compressor at two distinct speeds. One example of a motor useful in this modulation effort is shown and described in the copending application by Spradling, No. 723,990, filed Sept. 16, 1976, and assigned to the assignee of the present invention.
Multi-speed motors are well known in the art. In the past, multi-speed motors conventionally have been constructed by placing a plurality of distinct windings within a stator core, and thereafter switching between sets of distinct windings to vary motor speed. For the purposes of this specification, the term "distinct windings" means that each main winding pole of a dynamoelectric machine has a corresponding auxiliary winding pole used only in conjunction with its own main winding pole. With this type of motor construction, the number of main winding poles conventionally equals the number of auxiliary winding poles, the poles of the main and auxiliary winding being physically displaced with respect to one another in order to generate the revolving field of the induction device. While these multi-speed motors work well for their intended purposes, they generally have been used in applications where slot fills of the motors are not critical. "Slot fill" is a term of art, and generally refers to the slot area displaced by the turns of the motor winding divided by the total usable slot area, expressed as a percentage. In many induction motor applications, slot fills are not critical, and ample slot space is provided in the lamination design for carrying a number of motor windings in the slots of the stator assembly.
Hermetic motors, on the other hand, usually have slot fill concentrations that preclude multiple independent winding use. The high slot fills become necessary in order to achieve efficient motor operation in the first place. In general, motor performance can be improved by increasing the amount of material used in the windings or the stator core stack. Both of these design expedients are practiced extensively in hermetic motor design.
An additional factor involved in motor design for hermetic motors is the fact that the hermetic motor is enclosed and hermetically sealed within the compressor unit of the refrigeration system. Electrical connections are made through the shell of the compressor. The shell has a connection opening made in it, and a special connector that preserves the integrity of the refrigerant system is inserted in and hermetically seals the opening. The use and insertion of the connectors in the shells adds significantly to the compressor cost. Consequently, a general design requirement is that motors utilized in hermetic compressors use a minimum number of leads to minimize construction problems and the extra cost inherent in making multiple openings through the compressor shell to accommodate the electrical connectors.
The motor design disclosed hereinafter meets these stringent design criteria by providing a multiple speed motor having a minimum number of motor leads, which exhibits comparable performance at rated loads on either speed. In the preferred embodiment, the stator assembly of the motor has two independent main windings constructed from a plurality of coil sets inserted in the slots of the stator. The coil sets of the first main winding define two physical motor poles, while the coil sets of the second main winding define four physical motor poles. An auxiliary winding is provided, also constructed from a plurality of coil sets. The coil sets of the auxiliary winding define two physical poles, and the auxiliary winding is rotated physically with respect to the first main winding. When two pole motor operation is desired, the first main winding and the auxiliary winding are energized and the motor operates in a conventional manner as a two pole induction motor. When four pole operation is desired, the second main winding is energized, and the coil sets of the first main winding are reconnected so that the polarities of the two physical motor poles produce four electrical motor poles, the first main winding functioning as a second auxiliary winding for the second main winding of the motor.
Those skilled in the art will recognize that interconnection and energization of the windings may be accomplished automatically by suitable switching means. The arrangement disclosed utilizes a minimum number of windings, and requires only five external leads for passage through the compressor shell.
One of the objects of this invention is to provide a multi-speed induction motor having a first main winding, a second main winding, and a single distinct auxiliary winding, one of the main windings being reconnected to form a second auxiliary winding for the second main winding of the motor when the second speed operation is desired.
Another object of this invention is to provide a two speed hermetic motor for utilization in refrigeration compressors.
Yet another object of this invention is to provide a multi-speed hermetic motor having a minimum number of winding leads.
Another object of this invention is to provide a multi-speed motor where the breakdown torque of the motor, which is dependent upon the main winding, may be independently adjusted for each speed by adjusting each main winding.
Still another object of this invention is to provide an induction motor providing more efficient operation of a refrigeration system.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.